1. Field of the Invention
The present invention relates to a spot-size converter.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2007-93743 (Patent Document 1) discloses an optical waveguide having a spot-size conversion region. Without using a spot-size converter such as a thermally expanded core (TEC) fiber, an optical coupling with low loss can be provided between a high A optical waveguide and a single-mode optical fiber (SMF), both of which have different spot sizes. The optical waveguide having a spot-size conversion region includes an optical waveguide having a waveguide core and a ridge portion disposed at the fiber-coupled-end side of the optical waveguide. The ridge portion functions as the spot-size converter. The cross section of the ridge portion has a projecting shape. Furthermore, the width and height of the ridge portion decrease in a waveguiding direction from the fiber-coupled-end side.